Pertussis, also known as whooping cough, is a highly contagious respiratory tract infection caused by the bacterium Bordetella pertussis. This disease has been present throughout history, with documented outbreaks dating back to the 16th century. However, it was only in 1906 that Jules Bordet and Octave Gengou discovered the specific bacterium responsible for pertussis.
Transmission of pertussis primarily occurs through respiratory droplets when an infected individual coughs or sneezes. Others in close proximity can inhale the bacteria, leading to infection. Pertussis is highly infectious, with an estimated reproduction number (R0) of 12-17, meaning each infected individual can transmit the disease to 12-17 susceptible individuals.
Although pertussis can affect individuals of all ages, it is most severe in infants under one year old. Infants are especially vulnerable because they have not completed the full series of vaccinations. Pertussis can cause severe coughing fits, difficulty breathing, and in some cases, life-threatening complications. Older children and adults can also contract pertussis, but their symptoms are generally milder and may resemble a prolonged cough.
Globally, pertussis remains a significant public health concern. According to the World Health Organization (WHO), an estimated 24.1 million cases of pertussis occurred worldwide in 2019, resulting in approximately 160,700 deaths. However, these figures may be underestimated due to underreporting and limited resources for accurate diagnosis in many regions.
The burden of pertussis varies among different regions and populations. In high-income countries with robust immunization programs, the incidence of pertussis has significantly decreased. However, occasional outbreaks still occur, primarily affecting unvaccinated or incompletely vaccinated individuals and those with waning immunity. In low- and middle-income countries, pertussis remains a major cause of morbidity and mortality, especially in infants.
There are several risk factors associated with pertussis transmission:
1. Lack of Vaccination: Individuals who are unvaccinated or have not completed the recommended immunization schedule are at a higher risk of contracting pertussis.
2. Waning Immunity: Over time, the protection provided by the pertussis vaccine diminishes, making previously vaccinated individuals susceptible to infection.
3. Close Contact: Being in close proximity to an infected person, particularly in crowded settings like households, schools, or childcare facilities, increases the likelihood of transmission.
4. Age: Infants, especially those under six months old, face the highest risk of severe disease and complications. Adolescents and adults can also transmit the infection to vulnerable populations.
5. Maternal Transmission: Mothers with pertussis can transmit the infection to their newborns. Vaccination during pregnancy (preferably between the 27th and 36th weeks) can offer some protection to the newborn.
The impact of pertussis varies across regions and populations. In high-income countries, where vaccination coverage is high, pertussis rates have significantly declined compared to the pre-vaccine era. However, occasional outbreaks occur due to waning immunity or vaccine hesitancy. In low- and middle-income countries, pertussis remains a major public health issue, contributing to high infant mortality rates. Limited access to healthcare, inadequate immunization coverage, and challenges in diagnosis and treatment all contribute to the persistence of pertussis in these regions.
In conclusion, pertussis is a highly contagious respiratory tract infection caused by the bacterium Bordetella pertussis. It has a global prevalence, with millions of cases reported annually. Pertussis primarily affects infants, but individuals of all ages can be affected. Risk factors for pertussis transmission include lack of vaccination, waning immunity, close contact with infected individuals, and age. The impact of pertussis varies across regions, with higher-income countries experiencing lower prevalence rates compared to lower-income countries, where pertussis remains a substantial burden. Vaccination coverage and public health measures play a crucial role in reducing the transmission and impact of pertussis.

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Seasonal Patterns: The data provided reveals distinct seasonal patterns in the occurrence of Pertussis cases in mainland China. Generally, there is an upsurge in cases during the summer months (June to August) and a decrease during the winter months (December to February). This indicates that Pertussis experiences a peak season in the summer and a low season in the winter.
Peak and Trough Periods: The peak period for Pertussis cases in mainland China is July, with a substantial number of cases reported during this month. In contrast, the trough period occurs during January, February, and July, with the fewest number of cases reported.
Overall Trends: A closer look at the overall trends reveals an upward trajectory in Pertussis cases from 2010 to 2014, reaching its peak in 2014. Afterward, the number of cases fluctuates but generally remains high. It is worth noting that the number of cases starts to decline from 2020 onwards, with a significant decrease in 2021 and 2022. However, there is a notable surge in cases in July 2023, which potentially indicates a new wave of Pertussis cases.
Discussion: Pertussis in mainland China unmistakably displays seasonal patterns, with a peak during the summer and a low point during the winter. The overall trend demonstrates a rising number of cases until 2014, followed by a fluctuating pattern. The decline in cases in recent years suggests some success in control and prevention measures. However, the sudden increase in July 2023 raises concerns about a potential resurgence. Consequently, it is crucial to diligently monitor and maintain effective control measures against Pertussis in order to prevent further outbreaks and mitigate the impact of the disease.